Firearm with rear regulator

ABSTRACT

An M-4 type firearm is provided. The M-4 type firearm having a receiver with a bolt carrier movably located therein. A receiver extension is connected to the receiver with the receiver extension including a spring loaded bolt carrier buffer movable relative to the receiver for effecting return of the bolt carrier to a firing position of the bolt carrier. A regulator is provided on the receiver extension, for enabling movement of the bolt carrier buffer relative to the receiver and effecting automatic or semi-automatic fire when the receiver extension is at least partially filled with water.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No. 60/646,875 filed Jan. 25, 2005 which is incorporated by reference herein in its entirety.

BACKGROUND

1. Field

The exemplary embodiments disclosed herein relates to automatic or semi-automatic firearms and, more particularly, to automatic and semi-automatic firearms having a rear regulator.

2. Brief Description of Related Developments

The M-4 and M-16 type firearms, along with their commercial versions, are highly desired and widely distributed, around the world, among the law enforcement community, hunters and sporting users, as well as the military and paramilitary. Referring to FIGS. 1-2, there is respectively shown a perspective view of a conventional M-4 (or commercial A-4 variant) type firearm 1, and an expanded view of the firearm 1. As seen in FIGS. 1-2, the firearm 1 generally has a lower receiver 2, an upper receiver 4, a barrel 6 and stock 8. The upper receiver 4 is connected to the lower receiver 2. The barrel 6, which is covered by a handguard 10, is connected to the upper receiver 4. The upper receiver 4 holds the bolt carrier 12 that is operated by an operating system 14 powered by exhaust gases generated during firing of the firearm 1. As seen in FIG. 2, the lower receiver 2 may have a mounting bracket 2M for mounting a receiver extension 16. The receiver extension may be located within the stock and may provide support to the stock. In conventional M-4 type firearms, the receiver extension 16 is hollow and provides a housing for the action spring 18 and buffer assembly 20. The buffer assembly 20 is positioned by spring 18 against the bolt carrier 12, to bias the bolt carrier to its closed position. Hence, as may be realized, operation of the bolt carrier 12 (i.e. sliding back) inside the upper receiver under impetus from the operating system, impinges on the buffer assembly 20 thereby moving the buffer assembly back inside the receiver extension 16 and compressing the action spring 18. Conventional M-4 type firearms cannot be operated immediately after being immersed in water. However, there is a desire among operators for an M-4 type firearm capable of being fired substantially upon removal from water immersion. Further, as seen in FIG. 1, M-4 type firearms are provided with a safety or fire control selector 22 allowing an operator to select for example, between “Safe”, “Semi” (-automatic) and “Auto” (-matic) modes of operation. When in the “auto” mode of operation, the firing rate of conventional M-4 type firearms is not controllable by the operator. There is a desire for an M-4 type firearm having a controllable or selectable firing rate when operated in the “auto” mode. The exemplary embodiment disclosed herein overcomes, amongst other things, the problems of conventional M-4 type firearms.

SUMMARY OF THE EXEMPLARY EMBODIMENTS

In accordance with one exemplary embodiment, an M-4 type firearm is provided. The M-4 type firearm comprises a receiver with a bolt carrier movably located therein. A receiver extension is connected to the receiver with the receiver extension including a spring loaded bolt carrier buffer movable relative to the receiver for effecting return of the bolt carrier to a firing position of the bolt carrier. A regulator is provided on the receiver extension, for enabling movement of the bolt carrier buffer relative to the receiver and effecting automatic or semi-automatic fire when the receiver extension is at least partially filled with water.

In accordance with another exemplary embodiment, an M-4 type firearm is provided. The M-4 type firearm comprises a receiver with a bolt carrier movably located therein. A receiver extension is connected to the receiver, the receiver extension enclosing a bolt return spring. A regulator valve is coupled to the receiver extension. The bolt return spring effects return of the bolt carrier to a firing position. The regulator valve regulates a firing rate of the firearm.

In accordance with another exemplary embodiment, an M-4 type firearm is provided. The M-4 type firearm comprises a receiver having a bolt carrier movably located therein. A barrel is coupled to the receiver. A receiver extension is connected to the receiver, the receiver extension having a bolt return spring. An indirect gas operating system is coupled to the barrel. A cycle rate selector is coupled to the receiver extension. The indirect gas operating system cycles the bolt carrier from a firing position into the receiver extension. The bolt return spring effects return of the bolt carrier to the firing position. The cycle rate selector regulates a firing cycle rate of the firearm when in full automatic mode.

In accordance with another exemplary embodiment, an automatic firearm is provided. The automatic firearm comprises a receiver having a bolt carrier movably located therein. A receiver extension is connected to the receiver, the receiver extension having an interior passage through which the interior of the receiver communicates with the exterior of the firearm. A closure is coupled to the receiver extension, the closure being selectably movable between opened and closed position. The closure in the closed position is more restrictive on fluid flow through the interior passage than when the closure is in the opened position.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and other features of the present invention are explained in the following description, taken in connection with the accompanying drawings, wherein:

FIG. 1 is a perspective view of a firearm in accordance with the prior art;

FIG. 2 is an exploded perspective view of the prior art firearm in FIG. 1;

FIG. 3 is an elevation view of a firearm incorporating features of the present invention in accordance with an exemplary embodiment;

FIGS. 4A-4B are exploded perspective views of the lower receiver extension of the firearm in FIG. 3 with the receiver extension respectively shown in two different configurations;

FIGS. 5A-5B are partial exploded views of the end of the lower receiver extension in FIGS. 4A-4B respectively in different configurations;

FIGS. 6A-6B are end views of the lower receiver extension respectively in the different corresponding configurations shown in FIGS. 4A-4B;

FIGS. 7A-7C respectively are an end elevation view, a partial cross-sectional view and partial bottom view of the lower receiver extension;

FIGS. 8A-8D respectively are a perspective view and an elevation view, plan view and cross-sectional view of a regulator section of the firearm in FIG. 3;

FIG. 9A is an end view of an alternate embodiment lower receiver extension; and

FIG. 9B is an isometric view of an alternate embodiment regulator.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENT(s)

Referring to FIG. 3, there is shown, a side elevation view of an automatic firearm 30 capable of automatic or semiautomatic fire incorporating features in accordance with an exemplary embodiment of the present invention. Although the exemplary embodiments will be described with reference to the embodiments shown in the drawings, it should be understood that the exemplary embodiments can be embodied in many alternate forms of embodiments. In addition, any suitable size, shape or type of elements or materials could be used.

Firearm 30 is illustrated in FIG. 3 as an M-4 or M-16 type automatic firearm (or corresponding commercially available variant) for example purposes, and the present invention is applicable equally to any other desired type of firearm capable of automatic or semi-automatic fire. Firearm 30 may have operational features such as disclosed in U.S. Pat. Nos. 5,726,377, 5,760,328, 4,658,702 and 4,433,610, and U.S. patent application Ser. No. 10/836,443, filed Apr. 30, 2004 and U.S. Provisional Patent Application Ser. No. 60/564,895, filed Apr. 23, 2004, all of which are hereby incorporated by reference herein in their entirety. Firearm 30 incorporates features according to the present invention. The firearm 30 and its sections described in greater detail below is merely exemplary, and in alternate embodiments the firearm 30 may have other sections, portions or systems. Firearm 30 may incorporate a hand guard 40, a receiver section 42, a barrel 46, and stock 44. As will be described further below, hand guard 40 may further incorporate vent holes, ribbing, heat shields or double heat shields and liners to facilitate cooling of the barrel 46 while keeping hand guard 40 at a temperature sufficient for an operator. Hand guard 40 may have features such as disclosed in U.S. Pat. Nos. 4,663,875 and 4,536,982, both of which are hereby incorporated by reference herein in their entirety. Hand guard 40 and receiver section 42 may be configured to support such rails as a “Piccatiny Rail” configuration as described in Military Standard 1913, which is hereby incorporated by reference herein in its entirety. The handguard 40 may house a barrel radiator section for enhanced cooling of the barrel 46 such as for example disclosed in U.S. provisional application 60/610,703, filed Sep. 17, 2004 and incorporated by reference herein in its entirety. The barrel 46 of firearm 30 may also be provided with an active cooling system for example as also disclosed in U.S. provisional patent application 60/610,703 incorporated by reference herein.

As noted before, firearm 30 in this exemplary embodiment is an M-4 type automatic or semi-automatic firearm. Firearm 30 is thus, except as otherwise described below generally similar to firearm 1 shown in FIGS. 1-2 and described before. Hence, features of firearm 30 similar to features of firearm 1 will not be described in detail below. The bolt carrier 48 (see FIG. 3) in the upper receiver 50 of firearm 30 (similar to belt carrier 12 in the receiver of firearm 1, shown in FIG. 2) may be cycled by a suitable operating system. The operating system may be a direct gas operating system similar to operating system 14 shown in FIG. 2. In the exemplary embodiment, the operating systeM-480 (for cycling the bolt carrier 48) of firearm 30 may be an indirect gas operating system, a suitable example of which is disclosed in U.S. Provisional Application 60/610,703 previously incorporated by reference. The firearm 30 also has an action spring and buffer assembly similar to action spring 18 and buffer assembly 20 in FIG. 2, for motivating the return stroke of the bolt carrier 48 during its cycle. The action spring and buffer assembly of firearm 30 are housed (similar to spring and buffed assembly 18, 20 in FIG. 2) within the lower receiver rear extension 50. The lower receiver rear extension 50 of firearm 30, in the exemplary embodiment, has a regulator 52 capable of adjustment by the operator to enable firearm 30 to be fired substantially immediately upon removal from water or other fluid immersion, as well as provide a selectable firing rate when firearm 30 is operated in the “auto” mode as will be described in greater detail below.

Referring now also to FIG. 4A, there is shown an exploded view of the lower receiver extension 50 and regulator assembly 52. As seen in FIG. 4A, the receiver extension 50 has a hollow generally cylindrical shape. In alternate embodiments, the lower receiver extension may have any other desired shape. The front portion 50F of the receiver extension may have a suitable interface for coupling or otherwise interfacing the receiver extension to the receiver section 42 of firearm 30. For example, the front portion 50F of the receiver extension may incorporate a mechanical coupling, such as a threaded section similar to the threaded section at the front of the receiver extension 16 shown in FIG. 2. In alternate embodiments, the coupling of the receiver extension to the receiver section may have any other desirable interface. The receiver extension 50 may have a stock support 50S, as shown in FIG. 4A. The stock support 50S may provide a mount or attachment for the stock to the firearm receiver extension, and hence, facilitates mounting of the stock to the firearm. In this embodiment, the receiver extension may be a one-piece member of unitary construction with the integral stock support 50S. In alternate embodiments, the receiver extension may be an assembly. In the embodiment shown, the stock support 50S may be an elongated rail extending longitudinally on a bottom or ventral portion of the receiver extension. In alternate embodiments, the stock support may have any other suitable shape and any suitable orientation.

As seen in FIG. 4A, the receiver extension 50 has an end plate 54 at the rear portion 50R of the extension tube. The end plate 54 substantially closes, but does not completely seal the rear of the extension receiver tube. The end plate 54 defines part of the regulator or regulator valve 52 as will be described further below. Referring now also to FIGS. 7A-7C, there is respectively shown an end elevation, cross-sectional view, and partial bottom view of the rear portion of the receiver extension. The end plate 54 of the receiver extension 50 is seen best in FIGS. 7A-7B. In this embodiment, the end plate 54 may be integral to the unitary construction member forming the receiver extension 50. In alternate embodiments, the end plate may be a separate member, such as a separate end cap, that may be a mechanically fastened or otherwise bonded to the receiver extension tube. As seen in FIGS. 7A-7B, in this embodiment, the end plate has a port or aperture 62 extending therethrough. The port 62 in the end plate provides communication between the interior volume 50I in the receiver extension 50, where for example the action spring and buffer assembly are housed similar to spring 18 and buffer 20 in FIG. 2, and the exterior of the extension receiver. Port 62 in combination with interior volume 50I provide a passage through which the interior of the receiver communicates with the exterior of the firearm. In the embodiment shown, there are five ports 62 formed in the end plate 54. In alternate embodiments, any desired number of ports may be provided. The ports 62 may be formed by any suitable means, such as drilling through plate 54. The ports 62 may be of any suitable shape or size to allow desired level of communication between interior volume 50I and the exterior, as will be seen below, without adversely affecting the structural function of the end plate. For example, ports 62 may have a bore of about 0.125 inch diameter, though as noted before the ports may have any other suitable size bore. In alternate embodiments, the ports may have any desired shape and may not be a constant diameter bore. As seen in FIGS. 7A-7B, the ports 62 may be positioned in the lower portion 54L of the end plate. The ports 62 may be positioned proximate to the inner surface 501S of the extension tube as shown in FIG. 7B. In alternate embodiments, more or fewer ports may be provided in the lower portion of the end plate, and additional ports may be located in other areas around the periphery of the end plate. As seen in FIGS. 7A-7B, the end plate may be shaped/formed or machined to include an annular counter bore 56 from the rearmost face 54R of the end plate. The counter bore 56 is sized so that the ports 62 are located within the counter bore area. The counter bore 56 defines a peripheral rim 54P and a spindle or shaft 58. As seen in FIG. 7A, in this embodiment, the rim 54P extends substantially continuously around the perimeter of the counter bore 56, and may be sufficiently high (and conversely the counter bore may be sufficiently deep) to provide sufficient overlap with the valve assembly 72 (see FIG. 4A) of the regulator 52, as will be described below, to prevent undesired entry of contamination into the receiver extension interior 50I. Spindle 58 may have a bore 60 formed therein for a valve assembly mounting fastener (not shown).

The end plate 54 of the receiver extension is provided with a spring loaded detent 63 for positive engagement of the regulator valve assembly 72, in order to hold the valve assembly in a desired position (see FIG. 7A). In this embodiment, the spring loaded detent 63 may be located within the rim 54P of the end plate 54. As seen in FIG. 7B-7C, the spring loaded detent 63 may be located in bore 64. In this embodiment, the bore 64 housing the spring loaded detent may be formed through the stock support 50S to penetrate the inside face of the counter bore rim 54P. In alternate embodiments, the spring loaded detect may be provided in any other suitable location in the end plate or valve assembly. In this embodiment, bore 64 houses ball or pin 66, and a biasing spring (not shown) that biases the ball or pin 66 against shoulders 64S of bore 64. The detent ball/pin 66 is suitably shaped so that when biased against shoulders 64S, the ball/pin tip projects sufficiently beyond the rim inside face to securely engage the valve assembly disposed in the counter bore 56. A fastener or closure post (not shown) may be positioned in the bore 64 to secure the ball/pin 66 and spring inside the bore, and prevent undesired matter from entering the bore.

Referring now again to FIG. 4A, regulator 52 includes valve assembly 72. As may be realized from FIG. 4A, the valve assembly 72 is placed within the counter bore 56 of the end plate 54 to form regulator 52. Valve assembly 72 generally comprises valve 74, gasket 76 and a mounting fastener (not shown). As will be described, valve assembly 72 comprises a closure capable of being selectably moved between open and closed positions and between intermediate positions with the closed position closing the passage, at least in part. As will be described below, valve assembly 72 may operate as a variable firing cycle rate selector where the operator may select different firing rates as a function of the rotational position of valve 72. Valve 74 is shown in FIGS. 8A-8D. In this embodiment, valve 74 is shaped to conformally fit within the counter bore 56 in the end plate 64 of the receiver extension. The outer periphery 74P of the valve 74, or at least the front portion of the periphery 74P received within the rim 54P of counterbore 56, may have a diameter sized to form a close fit with the inside face of the rim 54P. As seen best in FIGS. 8B and 8D, the valve 74 has a bore 74B sized to receive and form a running fit with the spindle 58 (see FIG. 7B) of end plate 54. In the exemplary embodiment, valve 74 may be a one piece member of unitary construction. The valve 74 may be made of metal or plastic or any other suitable material. As seen in FIGS. 8A-8B and 8D, the valve 74 may have a hollowed portion 74I. In this embodiment, the hollow 74I extends inwards from the front face 74F of the valve 74, and has a generally semi-circular shape. The hollow is sized so that, when mated to the end plate 54 with the valve 74 positioned so that hollow 74I circumferentially overlaps, at least in part, one or more of the regulator ports 62, the radial width of the hollow is coextensive with the bore of the ports 62. In other words, the inner and outer radial edges 741L, 741M of the hollow are respectively outside the bore of the ports 62 in the end plate 54. The valve has ports 74A in the rear face communicating with the hollow 74I. The valve further may have outer ports 740 in the outer rim 74P of the valve that also communicate with the hollow 74I. In this embodiment, rear ports 74H may be formed by bores extending from the rear face 74R (as seen in FIG. 8D) into the hollow. Seven ports 74H are shown in FIG. 8B for example purposes, and in alternate embodiments more or fewer ports may be used of any desired size. The rear ports 74H may have a bore of about 0.125 inch diameter, though as noted above any suitable bore may be used. In this embodiment, there are a corresponding number (i.e. seven) of rim ports 740. The rim ports 740 are formed by suitable bores (e.g. about 0.125 diameter) extending radially inward from the outer rim 74P to the hollow 74I. As seen in FIG. 8C, the outer ports 740 are located on a resolution of the outer rim that is not located or overlapped by the rim lip 50P (see FIG. 7B) of the extension receiver when the valve 74 is mated to the end rate 54. In this embodiment, the bores for outer ports 740 may intersect the bores of the rear ports 74H. In alternate embodiments, the number, size and spacing of the outer ports may be altered as desired. In still other alternate embodiments, the valve may be provided with any desired combination of rear and outer ports including no rear ports, or no outer ports. As seen in FIG. 8D, the rear ports and outer ports respectively provide fluid flow paths, indicated by arrow RF, of respectively, for fluid in the hollow 74I subjected to positive head. The flow areas provided by the rear ports 74H and outer ports 740 may be larger than the flow area defined by the ports 62 in the end plate 54 of the extension receiver.

As seen in FIGS. 8A-8D, the portion of valve 74 opposite the hollow 74I is generally solid, so that when this portion of the valve 74 is positioned to cover the ports 62 in the end plate, the regulator is closed and fluid communication from the inside 50I of the receiver extension tube through ports 62 is blocked. In this embodiment, the front face 74F of the valve 74 has a blind slot 74G formed therein as shown in FIG. 8B. The blind slot 74G provides capture to gasket 76 (see FIG. 4A). The gasket 76, and hence slot 76G in the rear face of the valve is sized, so that when the valve 74 is positioned to the closed position, described below, the gasket covers all ports 62 in the end plate 54 of the receiver extension. Gasket 76 may be made of any suitable resiliently compliant material such as rubber, neoprene or composite. In alternate embodiments, the gasket, and capture space in the valve may have any other suitable shape and be located in any other suitable position. As seen in FIGS. 8B-8C, the outer rim 74P of the valve has engagement recesses 74E, 74EC for engagement of the spring loaded detent 63 in the end plate 54 (see FIG. 7C). The recesses 74EC, 74E are located on the periphery of the valve to provide the selectable positions of the regulator 52. Recess 74EC is located opposite the gasket holding recess 74G, and its position in cooperation with the location of the spring loaded detent 63 (see FIG. 7C) defines the regulator closed position. The other recesses 74E are located opposite the hollowing 74I and define different flow conditions for the regulator 52.

The regulator 52 is assembled by placing valve 74, with holding gasket 76 in slot 74G, into the counter bore 56 in the end plate 54 of the receiver extension 50. The valve 74 is positioned with its front face 74F against the extension receiver end plate. Accordingly, the hollow 74I and gasket 76 are facing the end plate. Spindle 58 is received in bore 74B so that the valve may be rotated clockwise/counterclockwise about the spindle. When the fastener (not shown) fastens the valve 74 to the end plate, the gasket 76 may be compressed against the inner surface of counter bore 56. As may be realized, the regulator 52 is controlled by rotating the valve 74 to the various positions defined by the engagement recesses 74E, 74EC. Referring now again to FIG. 4A, and also to FIG. 5A, which show the regulator 52 in the fully open position, where all the ports 62 in the receiver extension end plate are coincident or otherwise communicating without impediment with hollow 74I in the valve 74. In this position the recess 74EO in the valve is engaged by the spring loaded detent 63 stably holding the valve in the position relative to the receiver extension. The regulator fully open position is also shown in FIG. 6A. As seen in FIG. 6A, in this position the ports 62 in the receiver extension are within the coverage of the hollow 74I in the valve 74. As may be realized, as the valve 74 is rotated about the spindle 58 (see FIG. 7B) from the fully open position shown in FIG. 6A, the hollow 74I is rotated away from the ports 62, so that the ports become progressively misaligned with hollow 74I and blocked by gasket 76 in the valve 74. Continued rotation of valve 74, such as to an orientation about 180° from the fully open position in FIG. 6A, results in the gasket 76, in this embodiment, covering and hence closing all ports 62 in the receiver extension. In this position, illustrated in FIGS. 4B, 5B and 6B, the regulator 52 is closed. The engagement recess 74EC in the valve is engaged by the spring loaded detent 63, when the valve is in this position, to stably hold the valve closed. As described before, the valve 74 may be positioned in intermediate open positions as desired.

Thus, in the exemplary embodiment, the operator may readily control the regulator 52 by rotating valve 74 as desired. In the event the operator wishes to operate the firearm substantially immediately upon removal from water immersion, the operator may rotate valve 74 to fully open regulator 52 (position shown in FIG. 4A, 5A, 6A) as described before. This position provides for maximum fluid flow through the regulator. After the regulator 52 is opened, the operator may substantially immediately (for example within about two seconds or less from opening the regulator, or if the regulator is open prior to removal from immersion) commence to fire. The open regulator allows any water in the receiver extension to be discharged by the cycle action of the bolt carrier as well as standing water head. Any water may be discharged freely through the regulator with negligible effect on the cycle action of the bolt carrier. This is not possible with conventional firearms. Further, the operator may selectably adjust the cycle rate of the firearm with the regulator 52, when the firearm is operated in the automatic mode. As noted before, when fully open the regulator 52 allows the maximum fluid flow therethrough. As the regulator is progressively closed, by rotating valve 74 toward the fully closed position, the fluid flow rate through regulator 52 is progressively reduced. The minimum fluid flow through the regulator 52 is achieved when in the closed position. Air resistance in the receiver extension to the buffer as it is being moved by the bolt carrier cycle, and to the action spring as it is being compressed by the buffer correspondingly increases as the regulator goes from open to closed positions, with a commensurate but inverse affect (an air pressure resistance increases, cyclic rate decreases) on the cyclic rate of the firearm. The cyclic variance that may be achieve by controlling the regulator 52 between its open position and closed position may be about 40-50 cycles/second in the M-4 type firearm 30.

Referring now to FIG. 9A, there is shown an end view of an alternate embodiment lower receiver extension 80 having end plate 82. In this embodiment, the end plate 82 may be integral to the unitary construction member forming the receiver extension 80. In alternate embodiments, the end plate may be a separate member, such as a separate end cap, that may be a mechanically fastened or otherwise bonded to the receiver extension tube. End plate 82 has a port or aperture 84 extending therethrough providing fluid communication between the interior volume in the receiver extension 80, where for example the action spring 18 (shown dotted) and buffer assembly are housed similar to spring 18 and buffer 20 in FIG. 2, and the exterior of the extension receiver. In the embodiment shown, ports 84 are machined in receiver extension 80 radially closer to the center of receiver extension as compared to the embodiment shown in FIG. 7A. In doing so, spring 18 will not impede the flow of fluid through ports 84. In the embodiment shown, there are three ports 84 formed in the end plate 82; two of the ports being drilled diameters through with the central port being a machined kidney slot. In alternate embodiments, any desired number of ports may be provided in any number of shapes. For example, the ports may be a slot or combinations of any shape. As a further example, the ports may be cones or the diameters may have a radius on the entry and exit points to facilitate flow and minimize wear on the sealing surface of the regulator. The ports 84 may be formed by any suitable means, such as drilling through plate 84. The ports 84 may be of any suitable shape or size to allow desired level of communication between interior volume and the exterior without adversely affecting the structural function of the end plate. In alternate embodiments, more or fewer ports may be provided in the lower portion of the end plate, and additional ports may be located in other areas around the periphery of the end plate. Other features of receiver extension 80 may be similar to that of receiver extension 50.

Referring now to FIG. 9B, there is shown an isometric view of an alternate embodiment regulator 90. Regulator 90 has a generally hollowed portion 92 and a generally solid portion 94. Ports 106 are provided in hollowed portion 92. When hollowed portion 92 is positioned to cover the ports 84 in the end plate, the regulator is opened and fluid communication from the inside of the receiver extension tube through ports 84 is not blocked. When solid portion 94 is positioned to cover the ports 84 in the end plate, the regulator is closed and fluid communication from the inside of the receiver extension tube through ports 84 is blocked. When valve 90 is rotated at intermediate positions between the two aforementioned extremes, the flow through ports 84 is variably regulated from the two extremes. In this embodiment, the front face 94A of the valve 90 has a kidney shaped o-ring groove 96 formed therein. Groove 96 provides a seat for o-ring 98. The o-ring 98 and the corresponding groove 96 is sized, so that when the valve 90 is positioned to the closed position, the o-ring enclosed area covers all ports 84 in the end plate 82 of the receiver extension 80. o-ring 98 may be made of any suitable resiliently compliant material such as rubber, neoprene, viton or other suitable material or composite. In alternate embodiments, the o-ring, gasket, and capture space in the valve may have any other suitable shape and be located in any other suitable position or have multiple seals or sealing surfaces. The outer rim 100 of the valve 90 has engagement recesses 102A-102P for engagement of the spring loaded detent in the end plate 82. The recesses are located on the periphery of the valve to provide the selectable positions of the regulator 52. The recesses may have different depths, for example, to allow the user to know when in the full open or full closed position. Recesses may be provided at suitable locations, for example, to define different flow conditions for the regulator 90. In alternate embodiments, more or less recesses may be provided in alternate locations. In alternate embodiments, stops may be provided, for example to let the user know that the valve is at extremes of motion. A knurled surface 104 may be provided to allow the operator to rotate valve 90 without slippage.

It should be understood that the foregoing description is only illustrative of the exemplary embodiments. Various alternatives and modifications can be devised by those skilled in the art without departing from the exemplary embodiments. Accordingly, the exemplary embodiments are intended to embrace all such alternatives, modifications and variances which fall within the scope of the appended claims. 

1. An M-4 type firearm comprising: a receiver with a bolt carrier movably located therein; a receiver extension connected to the receiver, the receiver extension including a spring loaded bolt carrier buffer movable relative to the receiver for effecting return of the bolt carrier to a firing position of the bolt carrier; and a regulator, on the receiver extension, for enabling movement of the bolt carrier buffer relative to the receiver and effecting automatic or semi-automatic fire when the receiver extension is at least partially filled with water.
 2. The M-4 type firearm of claim 1, wherein, the regulator effects selection of a cycle rate of the bolt carrier between a first cycle rate and a different second cycle rate.
 3. The M-4 type firearm of claim 1, wherein, the regulator is selectably positionable in different selectable positions each of which effects a different firing rate of the firearm so that the firearm has a range of different firing rates, and wherein changing regulator position between different selectable positions changes the firing rate.
 4. The M-4 type firearm of claim 1, wherein, the regulator is selectably positionable to a sealed position, and wherein, the regulator in the sealed position seals an interior of the receiver extension to an exterior of the receiver extension.
 5. The M-4 type firearm of claim 1 further comprising a barrel coupled to the receiver and an indirect gas operating system coupled to the barrel, wherein, the indirect gas operating system cycles the bolt carrier from the firing position into the receiver extension.
 6. The M-4 type firearm of claim 1, wherein, the receiver extension further comprises an integral stock support.
 7. The M-4 type firearm of claim 1, wherein, the regulator comprises a rotatable selector coupled to the receiver extension, and wherein, the receiver extension further comprises a passage in fluid communication with the regulator, and wherein, the regulator is selectably positionable to effect selection of a firing rate from a range of different firing rates.
 8. An M-4 type firearm comprising: a receiver with a bolt carrier movably located therein; a receiver extension connected to the receiver, the receiver extension enclosing a bolt carrier return spring; and a regulator valve coupled to the receiver extension; wherein, the bolt carrier return spring effects return of the bolt carrier to a firing position, and wherein, the regulator valve regulates a firing rate of the firearm.
 9. The M-4 type firearm of claim 8, wherein, the regulator valve has different selectable settings corresponding to different selectable automatic firing cycle rates.
 10. The M-4 type firearm of claim 8, wherein, the receiver extension has at least one port interfacing with the regulator valve, and wherein the regulator valve regulates a fluid flow rate through the port.
 11. The M-4 type firearm of claim 8, further comprising a barrel coupled to the receiver and an indirect gas operating system coupled to the barrel, wherein, the indirect gas operating system cycles the bolt carrier from the firing position into the receiver extension.
 12. The M-4 type firearm of claim 8, wherein, the receiver extension has a port interfacing with the regulator valve, and wherein, the regulator valve is selectably positionable from a first position closing the port to a second position opening the port.
 13. The M-4 type firearm of claim 8, wherein, the regulator valve is capable of adjustment by an operator to enable the M-4 type firearm to be fired substantially immediately upon removal from water.
 14. The M-4 type firearm of claim 8, wherein, the regulator valve has a spring loaded engagement adapted to positively engage hold the regulator valve in a selectable position relative to the receiver extension.
 15. An M-4 type firearm comprising: a receiver having a bolt carrier movably located therein; a barrel coupled to the receiver; a receiver extension connected to the receiver, the receiver extension having a bolt carrier return spring; an indirect gas operating system coupled to the barrel; and a cycle rate selector mounted on the receiver extension; wherein, the indirect gas operating system and the bolt carrier return spring cooperate to cycle the bolt carrier in the receiver, and wherein, the cycle rate selector regulates automatic firing cycle rate of the firearm.
 16. The M-4 type firearm of claim 15, wherein, the cycle rate selector regulates gas flow within the receiver extension, and wherein, the gas flow results from the cycling bolt carrier.
 17. The M-4 type firearm of claim 15, wherein, the receiver extension has a plurality of ports interfacing with the cycle rate selector, wherein, the cycle rate selector is selectably positionable from a first position closing at least on port of the plurality of ports to a second position opening the at least one port, and wherein, the cycle rate selector further comprises a seal, the seal adapted to seal the at least one port when the cycle rate selector is in the first position.
 18. The M-4 type firearm of claim 17, wherein, when in the second position, the cycle rate selector enables movement of the bolt carrier effecting automatic or semi-automatic fire when the receiver extension is at least partially filled with water.
 19. The M-4 type firearm of claim 15, wherein, the receiver extension is of one piece unitary construction, and wherein the receiver extension further comprises an integral stock support.
 20. The M-4 type firearm of claim 15, wherein, the cycle rate selector comprises a valve having a gasket, the valve being rotatably coupled to the receiver.
 21. The M-4 type firearm of claim 15, wherein, the cycle rate selector comprises a valve having a port and a gasket, and wherein, the valve is rotatably coupled to the receiver, and wherein rotation of the valve variably regulates automatic firing cycle rate over a range of automatic firing cycle rates.
 22. An automatic firearm comprising: a receiver having a bolt carrier movably located in an interior of the receiver; a receiver extension connected to the receiver, the receiver extension having an interior passage through which the interior of the receiver communicates with an exterior of the firearm; a closure coupled to the receiver extension, the closure being selectably movable between opened and closed positions; wherein, the closure in the closed position is more restrictive on fluid flow through the interior passage than when the closure is in the opened position. 